Conventional Otto cycle internal combustion engines utilize spark ignition to ignite the fuel-air charge. There has been developed the so called "lean burn" engines, in which a very lean mixture is run to obtain various improvements in efficiency and emissions performance. Lean mixtures are difficult to ignite, and conventional spark ignition does not perform satisfactorily for such engines. Sophisticated stratified charge engines have been developed to solve the ignition problem by establishing a rich mixture in the region at which ignition occurs, but in effect this approach is a compromise of the improvements possible with a lean burn engine, and adds complexity in its implementation.
Another approach is to provide auxiliary combustion chambers in which a small quantity of a rich mixture is ignited to act as a torch in igniting the main charge.
This approach has entailed the use of extra valves to insure that the exhaust products are eliminated with each engine cycle.
High energy spark ignition systems have also been developed to solve the ignition problem, producing a jet of burning fuel, these devices referred to as, "plasma torch" ignitors. High currents in the arc relied on in these devices lead to excessive erosion of the electrodes across which the arc is discharged.
U.S. Pat. No. 4,757,788 describes the injection of fuel onto "make and break" electrodes between which an arc was previously established to ignite the fuel relied on to aid ignition of lean burn engines, which in effect operates as a stratified charge in having a localized rich mixture combustion.
U.S. Pat. No. 4,582,475, assigned to the same assignee as the present application describes "activation" of fuel by passing the fuel through a corona discharge and forming radicals of the fuel molecules to a concentration at which ignition of the fuel charge will occur upon introduction into an oxidizing atmosphere.
U.S. Pat. No. 4,672,938, also assigned to the same assignee as the present application, discloses activation prior to combustion by an electrical discharge including an electrical arc.
It is an object of the present invention to provide a torch ignition device for lean burn engines which does not require auxiliary combustion chambers or involve localized rich mixtures, or high voltage ignitors subject to high rates of electrode erosion.